Cholesteric liquid crystals have the property of selectively reflecting light of a specific wavelength, and in particular, they selectively reflect circularly polarized light in the same rotation direction as, and transmit circularly polarized light in the opposite direction to, the helical winding direction of the cholesteric liquid crystals.
In this type of cholesteric liquid crystal, in the prior art, it was reported that laser oscillation occurs at the edge of the selective reflection wavelength band (e.g., Non-patent document 1).
Recently, it has been proposed that in order to attain the laser oscillation with low-threshold value, the laser oscillation should be generated at a wavelength inside the selective reflection wavelength band, and various research has been pursued regarding laser oscillation elements which could generate this laser oscillation. A known example of such a laser oscillation element comprises two cholesteric liquid crystal films containing a dye or pigment (hereinafter “dye”) superimposed with different azimuth angles (e.g., Non-patent document 2).
Non-patent document 1: Kopp et al (4 others), “Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals”, Optics Letters, USA, 1998, Volume 23, p. 1707-1709.
Non-patent document 2: Ozaki et al (3 others), “Defect modes and laser oscillation in the stop band of cholesteric liquid crystals”, Journal of the Society of Electrical Materials Engineering, 2002, Volume 11 No. 2, page 165-167.